Hamburger A W, Pinnamaneni G
Program of Oncology/Department of Pathology, University of Maryland Cancer Center, Baltimore 21201.
Proc Soc Exp Biol Med. 1993 Jan;202(1):64-8. doi: 10.3181/00379727-202-43512.
Previous work from our laboratory has demonstrated that gamma-interferon (IFN) inhibits growth of the human breast carcinoma cell line MDA 468, while enhancing expression of epidermal growth factor receptor (EGFR). Epidermal growth factor at high levels is known to inhibit growth of this cell line. Because MDA 468 cells produce low levels of transforming growth factor (TGF)-alpha (a ligand for epidermal growth factor receptor), we reasoned that IFN-induced cytotoxicity could be partially mediated by enhanced secretion of TGF-alpha. Therefore, we determined the ability of IFN to modulate the endogenous expression of TGF-alpha by MDA 468 cells. IFN-gamma, at 500 units/ml, increased the levels of TGF-alpha in serum-free conditioned media of MDA 468 cells 3-fold as measured by radioimmunoassay. TGF-alpha mRNA was similarly increased approximately 3-fold after 5 days of IFN treatment as determined by dot blot and Northern analysis. IFN increased expression of TGF-alpha in conditioned media in a dose-dependent fashion. Increased secretion of TGF-alpha into conditioned media was not observed at Days 1 and 3. Similarly, increases in TGF-alpha mRNA were not observed at those time points. These results demonstrate that IFN-gamma enhanced secretion of TGF-alpha by MDA 468 cells. Although exogenous TGF-alpha inhibited MDA 468 cell growth, the role that the enhanced endogenous production of TGF-alpha plays in the cessation of cell growth induced by IFN remains to be determined.
我们实验室之前的研究表明，γ干扰素（IFN）可抑制人乳腺癌细胞系MDA 468的生长，同时增强表皮生长因子受体（EGFR）的表达。已知高水平的表皮生长因子可抑制该细胞系的生长。由于MDA 468细胞产生低水平的转化生长因子（TGF）-α（表皮生长因子受体的一种配体），我们推测IFN诱导的细胞毒性可能部分由TGF-α分泌增加介导。因此，我们测定了IFN调节MDA 468细胞内源性TGF-α表达的能力。通过放射免疫测定法测得，500单位/毫升的IFN-γ使MDA 468细胞无血清条件培养基中的TGF-α水平增加了3倍。通过斑点印迹和Northern分析确定，IFN处理5天后，TGF-α mRNA同样增加了约3倍。IFN以剂量依赖的方式增加条件培养基中TGF-α的表达。在第1天和第3天未观察到TGF-α分泌到条件培养基中的增加。同样，在这些时间点也未观察到TGF-α mRNA的增加。这些结果表明，IFN-γ增强了MDA 468细胞中TGF-α的分泌。尽管外源性TGF-α抑制MDA 468细胞生长，但内源性TGF-α产生增加在IFN诱导的细胞生长停止中所起的作用仍有待确定。
